Tuning device for lecher-wire systems



April 12, 1938. G. DE VRIES El AL TUNING DEVICE FOR LECHER WIRE SYSTEMS Filed Oct. 4, 1935 m E m NW M N R wwa m mm GM Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE TUNING DEVICE FOR LECHER-WIRE SYSTEMS Application October 4, 1935, Serial No. 43,490 In the Netherlands October 5, 1934 4 Claims.

The present invention relates to a Lecher-wire system which consists of two parallel conductors of even length and may be used for generating, transmitting and receiving high frequency and ultra-high frequency oscillations. The natural frequency of such a system depends on the effective length of the conductors. Consequently a variation in the tuning can be obtained by modifying the effective length of the conductors. This is frequently done by means of a contact bridge which is moved along a rail extending parallel with the Lecherwires. From a constructional point of view this method of tuning is seriously objectionable since the required rail is very cumbersome and must be arranged exactly parallel with the Lecher-wires.

The invention has for its purpose to provide a device having a simple construction for tuning a Lecher-wire system.

According to the invention both conductors of the Lecher-wire system are curved either over their Whole length or over part thereof in such a manner that the radius of curvature for both conductors is equal at corresponding points of 2 the latter, a movable contact bridge which is rotatable about a shaft being moved along the curved part of the conductors.

The invention will be more fully explained by reference to the accompanying drawing, the sole figure of which shows a preferred embodiment.

The conductors of a Lecher-wire system are provided with straight portions 1 and 2. These same conductors also have curved portions la and 2a and the radius of curvature thereof is substantially the same at all points. A contact bridge 3 is preferably supported by an arm 5 mounted on a shaft 4. This shaft is disposed coaxially with respect to the common axis of curvature of the two portions la and 2a. Upon rotation of the shaft 4 the contact bridge is moved along the curved part of the conductors la and 2a, thus modifying the effective length of the Lecher-wire system. The shaft 4 may be journalled in any suitable manner. Control of the positioning of the contact bridge may be had by turning the knob 6 which is fastened to one end of the shaft 4. It is clear that by centering the shaft 4 with respect to the axis of rotation of the semi-circular shaped wires in and 2a, the bridging member 3 will be rendered positionable at any suitable point for tuning the Lecher-wire system. It is also desirable that the straight portions l and 2 of the Lecher-wire system should be positioned radially with respect to the center of curvature of the members la and 2a. The reason for this is that the unused portions of the semi-circular members extending beyond the bridging member 3 will have the least possible reactive effect upon the energized portions of the system.

This arrangement has the advantage that the two conductors of the Lecher-wire system have always the same length and that the self-induction per unit of length of the system remains substantially unchanged, and because of the symmetry of the arrangement, undesirable reactances are avoided. This is particularly true in respect to an ultra-high frequency system Where every precaution must be taken in order to avoid undesirable reflections between used and adjacent unused portions of the conductive members. The apparatus itself is of simple design and readily constructed. Means for supporting the curved part of the conductors are superfluous, so that no extra dampings are involved.

We claim:

1. A device for tuning a Lecher-wire system comprising two parallel conductors of even length, each conductor being so curved over at least a portion of its whole length as to possess a uniform radius of curvature equal to that of the other conductor, a tuning control shaft, and a movable contact bridge mounted on and rotatable with said control shaft, said bridge being adapted to move along the curved portion of the conductors and to make contact therewith, said conductors and said bridge having a symmetrical formation such that a voltage node is developed at the center of the bridge, thereby to avoid undesirable reactances and reflections between used and unused portions of said conductors.

2. In an ultra-high radio frequency tuning system, an adjustable reactance comprising a pair of parallel conductors each conductor having a portion thereof conformed to the arc of a circle, a rotatable shaft axially disposed with respect to the two centers of curvature of said conductors, a bridging member adapted to engage with corresponding points on the two said conductors, means including an arm mounted on and radially extending from said shaft for carrying said bridging member, and manual control means for so turning said shaft with its arm and bridging member as to obtain a suit able adjustment of the inductive and capacitive values of said parallel conductors to the desired operating frequency of said tuning system.

3. In a radio frequency tuning system having an adjustable reaotance in the form of parallel conductors, portions at least of said conductors being arcuately disposed about a common axis, the method of selecting an appropriate combina tion of inductive and capacitive values for producing a desired resonance condition in said conductors which comprises conductively so bridging said conductors at suitable points of the arcuate portions thereof as to form a volt age node substantially midway between the conductors.

4. In a radio frequency tuning system having an adjustable reactance in the form of parallel conductors, portions of said conductors being straight and other portions arcuately disposed about a common axis, said axis being disposed in the plane in which the straight portions of said conductors lie, means for supporting said conductors and for providing a tuning control thereof, said means comprising a conductive bridge member adapted to contact with corresponding points on the arcuately formed portions of said conductors and rotative control means disposed coaxially with respect to the aforementioned common axis for moving said bridge member into any desired tuning position.

GERRIT DE VRIES.

HERMAN BERNARD RUDOLF BOOSMAN. 

